package oj;

import java.util.Scanner;

public class Day34S {
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        long[] arr=new long[90];
        arr[0]=1;
        arr[1]=2;
        for(int i=2;i<arr.length;i++){
            arr[i]=arr[i-1]+arr[i-2];
        }
        while(sc.hasNext()){
            int n=sc.nextInt();
            long f=arr[n-1];
            System.out.println(f);
        }
    }
}